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Evaluation Board for 2.7V to 5.25V, Micro Power, 8-Channel, 125 kSPS, 12-Bit ADC EVAL-AD7888CB

OPERATING THE AD7888 EVALUATION BOARD Power Supplies

FEATURES
Evaluation Board for 2.7V to 5.25V, Micro Power, 8-Channel, 125 kSPS, 12-Bit ADC EVAL-AD7888CB
Interfacing to this board is through a 96-way connector. This 96-way connector is compatible with the EVAL-CONTROL BOARD which is also available from Analog Devices. External sockets are provided for the AIN1-AIN8 inputs.
OPERATING THE AD7888 EVALUATION BOARD Power Supplies
Full-Featured Evaluation Board for the AD7888 EVAL-CONTROL BOARD Compatible Stand Alone Capability On-Board Analog Buffering and Reference Various Linking Options PC Software for Control and Data Analysis when used with EVAL-CONTROL BOARD
When using this evaluation board with the EVAL-CONTROL BOARD all supplies are provided from the EVALCONTROL BOARD through the 96 way connector. When using the board as a stand alone unit external supplies must be provided. This evaluation board has seven power supply inputs: VDD, AGND, +12V, -12V, AGND, DVDD and DGND. +5V / +3V must be connected to the VDD input to supply the AD7888 VDD pin. +12V and -12V are used to supply the OP467 quad op-amps and the AD780 voltage reference. 0V is connected to one or both of the AGND inputs. The DVDD input can be used to supply a separate +5V for the 74LS04 and the DGND input must be tied to 0V. Alternatively the 74LS04 can be supplied from the same +5V as the AD7888 supply by inserting LK15 . The supplies are decoupled to the relevant ground plane with 10µF tantalum and 0.1µF multilayer ceramic capacitors at the point where they enter the board. The supply pins of the AD7888, quad op-amps and reference are also decoupled to AGND with 10µF tantalum and a 0.1µF ceramic capacitor. Extensive ground planes are used on this board to minimize the effect of high frequency noise interference. There are two ground planes, AGND and DGND. These are connected at one location close to the AD7888.
INTRODUCTION
This Technical Note describes the evaluation board for the AD7888, high speed, low power, 12-bit ADC that operates from a single 2.7 V to 5.25 V power supply. The AD7888 is capable of a 125 ksps throughput rate. The input track-andhold acquires a signal in 500 ns and features a single ended sampling scheme. The AD7888 contains eight single-ended analog inputs, AIN1 through AIN8. The analog input on each of these channels is from 0 to VREF. The part is capable of converting full power signals up to 2.5MHz. Full data on the AD7888 is available in the AD7888 data sheet available from Analog Devices and should be consulted in conjunction with this Technical Note when using the Evaluation Board. On-board components include an AD780 which is a pin programmable +2.5V or +3V ultra high precision bandgap reference, three OP467 quad op-amps and a 74LS04 inverting buffer. There are various link options which are explained in detail on page 2.
FUNCTIONAL BLOCK DIAGRAM
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Information furnished by Analog Devices is believed to be accurate and reliable. However, no responsibility is assumed by Analog Devices for its use, nor for any infringements of patents or other rights of third parties which may result from its use. No license is granted by implication or otherwise under any patent or patent rights of Analog Devices.
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EVAL-AD7888CB
LINK AND SWITCH OPTIONS
There are 15 link options which must be set for the required operating setup before using the evaluation board. The functions of these options are outlined below.
Link No. Function.
LK1-LK8
These link options are used to connect the input of the 8 analog buffers the input sockets AIN1-AIN8 or to tie the analog buffer inputs to Agnd. LK1 is used for the AIN1 buffer and on to LK8 for the AIN8 buffer When one of these links is in position "A" the relevant AIN socket is tied to the input of the AIN buffer. When one of these links is in position "B" the relevant AIN buffer input is tied to Agnd. This link option controls the program pin of the AD780 voltage reference. When this link is "inserted" the AD780 output voltage is set to +3.0V. When this link is "removed" the AD780 output voltage is set to +2.5V. This link selects the the bias-up circuit. When this link is in When this link is in When this link is in source of the reference voltage applied to both the AD7888 REFIN / OUT pin and to position "A" the output of the AD780 is selected. position "B" an external reference can be applied via the SMB socket, J6. position "C" the AD7888 internal reference can be used.
This link is used to select a 50 termination on the input of the bias-up circuit. When this link is "inserted" the 50 termination is applied. When this link is "removed" the 50 termination is removed. This link selects the source of the Vdd supply to the AD7888. from the EVAL-CONTROL BOARD. When this link is in position "A" the VDD must be supplied from an external source via J2 . When this link is in position "B" the VDD is supplied from the EVAL-CONTROL BOARD This link option is used to select the source of the +12V supply In position A, the +12V is supplied from the EVAL-CONTROL BOARD through the 96 way connector. In position B, the +12V is supplied from an external source through the power connector, J3. This link option is used to select the source of the -12V supply. In position A, the -12V is supplied from the EVAL-CONTROL BOARD through the 96 way connector. In position B, the -12V is supplied from an external source through the power connector, J3. This link selects the source of the DVDD +5V supply for the 74LS04 digital buffers. When this link is "inserted" it is supplied from the same power source supplying the AD7888 VDD pin. When this link is "removed" power must be supplied from an external source via the power connector, J7.
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SETUP CONDITIONS
Care should be taken before applying power and signals to the evaluation board to ensure that all link positions are as per the required operating mode. Table I shows the position in which all the links are set when the evaluation board is sent out.
Table I. Initial Link and Switch Positions
Link No. LK1 LK2-LK8 LK9 LK10 LK11 LK12 LK13 LK14 LK15
Position A B Removed A Inserted B A A Inserted
Function. AIN1 SMB connected to the input of the relevant analog buffer. The inputs of the AIN2 - AIN8 analog buffers are tied to AGND. AD780 is set to provide a +2.5V reference. AD780 is selected to supply the reference voltage for the AD7888. 50 termination resistor is applied to the input of the bias-up circuit. VDD for the AD7888 is supplied by the EVAL-CONTROL BOARD via J1. +12V supplied from EVAL-CONTROL BOARD via J1. -12V supplied from EVAL-CONTROL BOARD via J1. 74LS04 is powered from the same power source as the AD7888.
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EVALUATION BOARD INTERFACING Table II. 96-Way Connector Pin Functions. ROWA ROWB ROWC
Interfacing to the evaluation board is via a 96-way connector, J1. J1 is used to connect the evaluation board to the EVALCONTROL BOARD or other system. The pinout for the J1 connector is shown in Figure 2 and its pin designations are given in Table II.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 AVDD AVDD AVDD AGND -12V DGND AGND AGND AGND AGND AGND AGND DGND AGND AGND AGND AGND AGND AGND AGND AGND AGND AGND AGND +12V DGND AGND AGND AGND AGND AGND AGND DGND DGND DGND DGND DGND DGND DGND DT0 TFS0 DGND DGND DR0 RFS0 SCLK0
Figure 2. Pin Configuration for the 96-Way Connector, J1
96-Way Connector Pin Description
DTO DRO
Data Transmit Zero. This output is connected to the DIN pin of the AD7888. Data Receive Zero. This input is connected to the DOUT pin of the AD7888 via two inverting buffers. Serial Clock Zero. This serial clock is connected to the SCLK pin of the AD7888 via an inverting buffer. Transmit / Receive Frame Sync Zero. These two outputs are connected to the CS pin of the AD7888. Digital Ground. These pins are connected to the digital ground plane on the evaluation board. It allows the user to provide the digital supply via the connector along with the other digital signals. Analog Ground. These pins are connected to the analog ground plane on the evaluation board. Analog VDD Supply. These pins are connected to the VDD pin of the AD7888 via LK12. +12V Supply. This pin is connected to the V+ supply line on the board via LK13. -12V Supply. This line is connected to the V- supply line on the board via LK14.
SCLK0
TFSO / RFS0
+12V -12V
Note : The unused pins of the 96-way connector are not shown.
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SOCKETS OPERATING WITH THE EVAL-CONTROL BOARD
There are eleven input sockets relevant to the operation of the AD7888 on this evaluation board. The function of these sockets is outlined in Table III.
Table III. Socket Functions
Socket AIN1 AIN2 AIN3 AIN4 AIN5 AIN6 AIN7 AIN8 J4 J5 J6
Function Sub-Miniature BNC Socket for AIN1 channel. Sub-Miniature BNC Socket for AIN2 channel. Sub-Miniature BNC Socket for AIN3 channel. Sub-Miniature BNC Socket for AIN4 channel. Sub-Miniature BNC Socket for AIN5 channel. Sub-Miniature BNC Socket for AIN6 channel. Sub-Miniature BNC Socket for AIN7 channel. Sub-Miniature BNC Socket for AIN8 channel. Sub-Miniature BNC Socket for Analog input to bias-up circuit. Sub-Miniature BNC Socket for Analog output from bias-up circuit. Sub-Miniature BNC Socket for external reference voltage input.
The evaluation board can be operated in a stand-alone mode or operated in conjunction with the EVAL-CONTROL BOARD. This EVAL-CONTROL BOARD is available from Analog Devices under the order entry "EVAL-CONTROL BOARD". When operated with this control board, all supplies and control signals to operate the AD7888 are provided by the EVAL-CONTROL BOARD when it is run under control of the AD7888 software which is provided with the AD7888 evaluation board package. This EVAL-CONTROL BOARD will also operate with all Analog Devices evaluation boards which end with the letters CB in their title. The 96-way connector on the EVAL-AD7888CB plugs directly into the 96-way connector on the EVAL-CONTROL BOARD. No power supplies are required in the system. The EVAL-CONTROL BOARD generates all the required supplies for itself and the EVAL-AD7888CB. The EVAL-CONTROL BOARD is powered from a 12V ac transformer. This is a standard 12V ac transformer capable of supplying 1A current and is available as an accessory from Analog Devices under the following part numbers: EVAL-110VAC-US: EVAL-220VAC-UK: EVAL-220VAC-EU: For use in the U.S. or Japan For use in the U.K. For use in Europe
These transformers are also available for other suppliers including Digikey (U.S.) and Campbell Collins (U.K.). Connection between the EVAL-CONTROL BOARD and the serial port of a PC is via a standard RS-232 cable which is provided as part the EVAL-CONTROL BOARD package. Please refer to the manual which accompanies the EVAL-CONTROL BOARD for more details on the EVALCONTROL BOARD package.
CONNECTORS
There are four connectors on the AD7888 evaluation board as outlined in Table IV.
Table IV. Connector Functions
Connector J1 J2 J3 J7
Function 96-Way Connector used to interface to EVALCONTROL BOARD External VDD & AGND power connector. External +12V, -12V & AGND power connector. External DVDD & DGND power connector.
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Figure 3. Main Screen
SOFTWARE DESCRIPTION
Included in the EVAL-AD7888CB evaluation board package is a PC-compatible disk which contains software for controlling and evaluating the performance of the AD7888 when it is operated with the EVAL-CONTROL BOARD. The EVAL-AD7888CB Demonstration / Evaluation Software runs under DOS 4.0 or later and requires a minimum of a 386-based machine with 400kB of base RAM and 500kB of free hard disk space. The user interface on the PC is a dedicated program written especially for the AD7888. The disk which accompanies the EVAL-AD7888CB contains several files. The user should create a new directory on the main PC drive and label this "AD7888". Then, all files on the EVAL-AD7888CB disk should be copied into this directory. The Mouse Driver on the PC should be enabled before running the software. If this has not been loaded, the program will not run. To run the software, simply make the AD7888 directory the current directory and type "go". When the evaluation program starts, the user sees the screen shown on Figure 3 (without any FFT or scope waveforms). This is the main screen and it is divided into three parts. The top part provides the main control interface for the AD7888 evaluation software. The middle part of the main screen functions as a Digital Storage Oscilloscope and the bottom part of the main screen operates as either a Digital Spectrum Analyzer or a Histogram analyzer. Each part of the screen has several buttons that can be pressed by using the mouse or the keyboard. To press a button using the mouse, simply use it to move the on-screen pointer to the button to be activated and click. To use the keyboard, simply press the appropriate key as highlighted on the button. Lower -6-
case letters must be used. When a button is pressed, it is highlighted on the screen. The next button can be highlighted by using the Tab key or the previous button by holding down the shift key and the Tab key together. The highlighted button can also be pressed by pressing the space bar. Pressing the ESC key halts any operation currently in progress. In this document, if a button can be activated from the keyboard then the key used is shown in bold in the button name. For example, "no prog" has the "p" highlighted in bold, indicating that the button can be activated by pressing the p key. Some buttons have a red indicator. A red indicator on the button means that the function associated with that button is on. Absence of the red indicator light means that the function associated with the button is off. The on / off status of these buttons is changed simply by selecting the button.
Setting up the EVAL-CONTROL BOARD
When the software is run, the "F2 Setup" button in the top left of the screen should be selected to pop up the setup menu (see fig. 4). This menu sets up the EVAL-CONTROL BOARD for use with the EVAL-AD7888CB. Firstly, the configuration file must be loaded. The configuration file contains the default configuration information for the EVAL-CONTROL BOARD, the Digital Spectrum Analyzer and the Digital Storage Oscilloscope. It also tells the AD7888.EXE software which .HIP file to download to the ADSP-2111. The .HIP file contains the DSP code which is executed by the ADSP-2111. Normally, the "no prog" button is off, so when the configuration file is loaded, the .HIP file is automatically downloaded to the ADSP-2111. However, if the "no prog" button is on, then the .HIP file is not downloaded to the ADSP-2111. REV. A
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To load the configuration file, click the "load" button on the screen. After the configuration file is loaded, the sample rate and number of samples can be changed. Due to the nature of the software, the maximum sampling rate allowed is limited in each operating mode. In mode 2, the maximum sampling rate is 68KHz and in mode 3 and mode 4 it is 43KHz. If mode 2 operation only is required, then the sample rate can be increased to a maximum of 100KHz with a slight change in the software. Please contact GP.APPS@analog.com for this information. F5: Save. This saves a set of samples to a file for use either at a later date or with other software. The samples can be saved either as "volts", "ints" or "binary". The format of all these files is ASCII text. Note that the AD7888 software can only load files saved in the "ints" format. Files saved in the "volts" and "ints" formats can be used with packages such as Mathcad. Files saved in the "binary" format are for viewing purposes only. Load. This allows the user to load data from a file with a .DAT extension. Only data that was saved as ints can be loaded and analyzed. A configuration file must be loaded via the "F2 Setup" menu before the data file can be analyzed. If there is no EVALCONTROL BOARD connected to the PC, then the "no prog" button in the "F2 Setup" menu must be on. Once a configuration file has been loaded, the data loaded from the .DAT file is analyzed according to the settings in the "F2 Setup" menu. Reset. Choosing this option resets the EVAL-CONTROL BOARD. Quit. This quits the AD7888 evaluation software and returns control to the operating system.
F7: F10:
INFORMATION WINDOWS
Figure 4. Setup Menu Screen
The analog input channel is selected by clicking on the required channel and the reference can be turned off / on by clicking on the reference button. The required mode of operation is selected bt clicking on one of the 4 buttons in the "Power" section. Refer to data sheet for complete explanation of these operational modes. The "Analog in" section shows the analog input range and DC offset voltage. The "Coding" section is set to Unipolar by default when a configuration file is loaded. It should never be set to Bipolar when evalualauting te AD7888.
MAIN SCREEN
There are three information windows at the top of the main screen. The left-hand window is the configuration window and gives details about part being evaluated. It shows the name of the program that has been downloaded to the EVALCONTROL BOARD, the sampling frequency, the number of bits, the analog input range of the part and the output code format of the part. The right-hand large window is the Status window. This window provides feedback to the user as to what operations are currently being performed by the software and also displays error messages. Directly underneath the status window is a small window that shows the selected conversion sequence and the maximum and minimum values of the most recently captured samples for all channels in the conversion sequence.
Test Mode
The top left part of the main screen contains eight buttons which are selected using the mouse or by using the function keys from the keyboard. These buttons and the actions they perform are: F1: F2: F3: Info. This button shows information on the software. Setup. This button activates the setup menu. Samp. When this key is pressed, the software causes the AD7888 to perform a number of conversions as determined by the setup menu (see above). The data from these conversions is then analyzed by the AD7888 evaluation software. Another set of samples may be taken by pressing the F3 key again. Cont. Pressing this button causes the software to repeatedly perform conversions and analyze them. Once the conversions and analysis has been done for one set of samples, the software automatically repeats the process. It continues to do this until the ESC key is pressed. -7-
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DIGITAL STORAGE OSCILLOSCOPE.
moved and the signal is displayed with its horizontal axis corresponding to a code of 0. The ac display option is useful for zooming in on a lowlevel signal that has a large dc offset. When the "dual" button is on, the oscilloscope screen is divided into two parts with the sampled data display centered on one horizontal axis and the windowed data display centered on another. When the "dual" button is off, both traces are centered on the same horizontal axis. This button toggles the sampled data trace on and off. This button toggles the windowed data trace on and off.
HISTOGRAM ANALYZER
The histogram analyzer counts the number of occurrences of each code in the captured samples and displays a histogram of these counts. The most frequently occurring code is displayed in the center of the histogram. The analyzer is normally used with a dc input signal and calculates the mean and the standard deviation of the sampled data. The mean and standard deviation are displayed in both volts and in units of the lsb size of the converter. The histogram gives a good indication of the dc noise performance of the ADC. The standard deviation shows directly the noise introduced in the conversion process. Each channel is the sequence can be viewed in turn using the 4 channel select buttons on the right of the histogram screen
Figure 5 Histogram Screen
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Figure 6. AD7888 Evaluation Board Circuit Diagram
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Table V. AD7888 Evaluation Board Bill Of Materials
Reference Designator U1 U2 U3 U4 U5 U6 C1 - C8 C9 12 17 19 21 23 25 27 29 31 39 44 C10 C36
Description OP467 Quad op-amp AD7888 ADC AD780 Voltage Reference 74LS04 Hex invertor 10nF NPO Capacitor (1206 case) 10uF 16V Tantalum (TAJ-B Case) 0.1uf X7R Ceramic (0603 Case)
Manuf / Dist ADI ADI ADI Farnell Farnell Farnell Farnell Farnell Farnell Farnell Farnell Farnell Farnell Farnell ITT Cannon Farrnell Farnell Farnell Farnell Farnell Farnell Farnell Farnell Farrnell Farnell
Part No. OP467GP AD7888BR AD780AN FEC 373-450 FEC 578-320 FEC 498-737 FEC 499-675 FEC 499-687 FEC 498-798 FEC 499-225 FEC 237-024 FEC 543-070 FEC 339-635 FEC 339-179
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Figure 7. Component Side Artwork
Figure 8. Solder Side Artwork
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Figure 9. AD7888 Evaluation Board Component Placement Drawing.